Author: Vincent Diepeveen
Date: 07:03:33 04/07/04
Go up one level in this thread
On April 07, 2004 at 09:19:13, martin fierz wrote: >On April 07, 2004 at 09:14:42, Vincent Diepeveen wrote: > >>On April 07, 2004 at 08:27:59, martin fierz wrote: >> >>>On April 07, 2004 at 06:49:59, Renze Steenhuisen wrote: >>> >>>> >>>>Hi all, >>>> >>>>could someone give me some numbers that are common with hashkey collisions? >>>>Because I guess my % is little too high... >>>> >>>>I'm getting like 0.03% [which is 1 every 3000, if I'm not mistaken] >>>> >>>>This is when using TT=32MB (haven't got the exact number of entries) >>>> >>>>If you think it is an error, any suggestions on where to start looking? >>>> >>>>Thanks! >>>> >>>> Renze >>> >>>hi renze, >>> >>>your number is much too high. a good estimate for the hash collision probability >>>is 1/sqrt(hashkey_range); which in your case comes out as 2^-32 or about >>>somewhere around one in a billion... >> >>Not at all. It's way less than that with 64 bits Zobrist. > >i never took the trouble to measure it, but the math is rather straightforward. >so i'd say you have an implementation bug too ;-) You do not store 64 bits i bet but just like 32 bits or so and use the rest for index. So effectively having like 60 bits at most. Note that i also store the color in a special bit. So i had a garantueed 65 bits in DIEP. Note that i write i 'had'. >cheers > martin > >>I measured it with 460 processors at a supercomputer with a shared hashtable and >>had major problems to get at 7 million nodes a second stored, some >>errors/collissions. >> >>>make sure you're not doing anything wrong with the hashkey updating like >>>suggested by others - compare with a computed-from-scratch key. also make sure >>>that your nullmove doesn't break your hashkey. and just to be sure, check that >>>you haven't got 32-bit numbers instead of 64 bit numbers by accident... >>>cheers >>> martin >> >>I'm sure it was some implementation bug with Renze.
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